1. Industrial Field of Utilization
The present invention relates to the construction of a membrane type magnetic head for use in a magnetic disc apparatus.
2. Description of Prior Arts
FIG. 1 is a sectional view of a membrane type magnetic head according to a prior art as disclosed, for example, in Japanese Patent Laid-Open No. 61-110320. In FIG. 1, numeral 1 designates a substrate made of Al.sub.2 O.sub.3 -TiC, etc., numeral 2 a lower magnetic layer formed on said substrate 1 in a predetermined pattern and made of Ni, Fe, etc., numeral 3 an insulating gap layer formed on said lower magnetic layer 2 and made of SiO.sub.2, A1.sub.2 O.sub.3, etc., numeral 41 a first resin-made insulating layer formed by thermosetting resist material or the like in a specified area on the substrate 1 on which said lower magnetic layer 2 and insulating gap layer 3 have beeb formed, numeral 5 a coil conductor layer made of Cu, etc. formed in a specified pattern on said first resin insulating layer 41, numeral 42 a second resin insulating layer formed of resist material, etc., and numeral 6 an upper magnetic layer made of Ni, Fe, etc. formed in a specified pattern on the upper surface of the laminate comprising said lower magnetic layer 2, said insulating gap layer 3, said first and second resin insulating layers 41, 42 and so forth. Numeral 7 designates a protecting layer formed on said upper magnetic layer 6 and the associated second resin insulating layer 42 and is made of SiO.sub.2, Al.sub.2 O.sub.3 or the like.
The operation of said prior art magnetic head will next be explained. In a magnetic disc apparatus, when information is written on a magnetic disc representing the magnetic recording medium, signal current is caused to flow through the coil conductor layer 5 of a membrane type magnetic head to generate magnetic flux to pass through the lower magnetic layer 2 and upper magnetic layer 6. When the magnetic disc is placed near the leakage flux formed at the tip and portion (or the extreme lefthand portion of the drawing) of the lower magnetic layer 2 and the upper magnetic layer 6 which sandwich the insulating gap layer 3, the magnetic layer of the magnetic disc is magnetized in accordance with the direction and the intensity of the leakage flux of said membrane type magnetic head so that information may be recorded. Conversely when information leaks out of the magnetic disc in which said information was recorded, the magnetic flux of the magnetic disc is picked up by the tip end of the magnetic layer of the membrane type magnetic head, and any voltage change which may occur at the opposite ends of the coil conductor layer 5 due to electromagnetic induction of the magnetic flux flowing through the lower magnetic layer 2 and the magnetic layer 6 is converted into signals which are in turn read.
In the membrane type magnetic head of prior art, various materials are laminated to form the head. The first and second resin insulating layers 41, 42 have low thermal conductivity, a high thermal expansion coefficient and a highly hygroscopic nature compared to the other layers 3, 5, 6 which are made of metallic or inorganic materials. Accordingly when the volume of the first and second resin insulating layers 41, 42 is increased due to the effect of temperature and humidity when said membrane type magnetic head is used or tested and the signal generated by current flowing through the coil conductor layer 5, the upper magnetic layer 6 and the protecting layer 7 which are formed adjacent to the first and second resin insulating layers 41, 42 will be adversely affected. In other words, when the upper magnetic layer 6 is distorted by pressure, the magnetic zone of the upper magnetic layer 6 is also distorted due to the resulting magnetic distortion effect. As a result, such problems as deterioration of the electromagnetic conversion characteristics of the membrane type magnetic head and cracking of the protecting layer 7 due to pressurization may result.